For example, JP-A-10-002706 discloses a linear displacement detection apparatus. As shown in FIG. 25, the conventional linear displacement detection apparatus is configured to convert one-dimensional displacement (linear displacement, linear motion) of a shaft 101 into a rotary displacement (rotary motion) of a sensor lever 104 so as to detect the linear displacement. The sensor lever 104 is fixed to a sensor rotor of a rotation angle sensor 102. The sensor lever 104 has one end at the side of the sensor rotor, and the one end is rotatably and pivotally supported by a rotation axis 103 of the rotation angle sensor 102. The sensor lever 104 has the other end at the side of the shaft 101, and the other end has an elongated hole 105. The elongated hole 105 is screwed with a contact portion 111 of the shaft 101.
The rotation angle sensor 102 accommodates a sensor rotor and a printed circuit board. Together with the sensor lever 104, the sensor rotor is provided to the rotation axis 103. The printed circuit board is opposed to the sensor rotor. An arc-shaped resistive element pattern and an arc-shaped conductive element pattern are provided on the printed circuit board. The arc-shaped resistive element pattern is coaxial with the arc-shaped conductive element pattern. The sensor rotor is provided with a brush, which electrically conducts the resistive element pattern with the conductive element. The rotation angle sensor 102 as a displacement sensor is configured to convert the rotation angle of the sensor rotor into an electric signal and output the electric signal. The rotation angle sensor 102 is configured to detect the linear displacement (shaft displacement, present position) of the shaft 101.
In the conventional linear displacement detection apparatus, in the case where the shaft 101 is exerted with a radial rock in addition to linear displacement, the radial rock of the shaft 101 exerts torsion to the sensor lever 104. Consequently, the radial rock of the shaft 101 acts as the linear displacement of the shaft 101 and causes an error of the linear displacement of the measurement of the shaft 101. In this case, rocking of the shaft 101 exerts torsion to the sensor lever 104. Consequently, the rocking of the shaft 101 applies load to the sensor lever 104. Thus, the sensor lever 104 needs sufficient strength against cyclic stress caused by the load. Furthermore, in a structure where the rotation axis 103 of the rotation angle sensor 102 is located in an offset manner with respect to the sensor rotor and the shaft 101, the sensor lever 104 is supported by one side. In this case, the sensor lever 104 is twisted when transmitting the displacement of the shaft 101, and hence the twist of the sensor lever 104 cause an error in detection of the linear displacement of the shaft 101. Furthermore, in the conventional linear displacement detection apparatus, the contact position between a contact portion 111 of the shaft 101 and the elongated hole 105 of the sensor lever 104 may change, and distortion occurs in the contact position when the linear displacement of the shaft 101 is converted into the rotary displacement of the sensor lever 104.
In the conventional linear displacement detection apparatus, distortion caused in the conversion of the linear displacement of the shaft 101 into the rotary displacement of the sensor lever 104 is released by changing the physical relationship between the contact portion 111 of the shaft 101 and the elongated hole 105 of the sensor lever 104. That is, the distortion is released by changing the turning radius (R) of the sensor lever 104 using the elongated hole 105. In this case, as the turning radius (R) of the sensor lever 104 becomes large, the change in the rotation angle of the sensor lever 104 with respect to the linear displacement of the shaft 101 becomes small. Alternatively, as the turning radius (R) of the sensor lever 104 becomes small, the change in the rotation angle of the sensor lever 104 with respect to the linear displacement of the shaft 101 becomes large. Accordingly, when the turning radius (R) of the sensor lever 104 changes, the relationship between the linear displacement of the shaft 101 and the rotation angle of the sensor lever 104 becomes nonlinear. Consequently, detecting accuracy of the linear displacement of the shaft 101 is impaired.